Metal stack etching using a helical resonator plasma

Abstract
A low-pressure etching process for advanced aluminum metallization stacks was developed using a high-density helical resonator plasma source (Prototech model ESRF 600) mounted on a Lucas Labs cluster tool. The metallization stacks consisted of a 300 Å TiN antireflection layer on 6000 Å of Al (1% Cu) with a 1000 Å TiN diffusion barrier and a 100 Å Ti film to enhance adhesion to the underlying SiO2. The features widths were as small as 0.45 μm. The films were etched using gas mixtures of Cl2/BCl3. The BCl3 proved to be an important additive to reduce notching of the Al film at the interface between the Al and the top layer of TiN. Best feature profiles were obtained using 80–90 sccm Cl2 and 10–20 sccm BCl3 at the following reactor conditions: 2.0 mTorr, wafer platen temperature T=0 °C, 100 W rf bias power, and 1500 W source power. More anisotropic profiles are obtained by either decreasing the wafer platen temperature or increasing the rf-bias power. The photoresist is also stripped in the same process chamber using an oxygen plasma at 5 mTorr, 50 W rf-bias power, and 1500 W source power at a chuck temperature of 25 °C. Extensive application of real-time process diagnostics, including optical emission spectroscopy and full wafer interferometry, aided process development by identifying end points, etching rates, and etching rate uniformities.

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